Sean Pierson was born on 10 March, 1976 in Toronto, Ontario, Canada. Pierson began wrestling at age 8. He continued wrestling throughout high school and into University. He attended Brock University in St. Catharines, Ontario, one of the best wrestling universities in Canada. Pierson stills occasionally visits Brock University and their wrestling team.  Pierson was a member of the Canadian National Team in Greco-Roman and Freestyle. He won multiple national championships in Greco-Roman and the Canadian University National Freestyle Championship. During his high school years, Pierson also began studying Judo.

Pierson was signed to Bellator in 2010 and planned to fight in Bellator's Second Welterweight Tournament Season, but was forced out of the tournament due to injury. Before making his Bellator debut at Bellator XV, Pierson signed to the UFC.

It was announced on 27 October, 2010 that Pierson would be filling in for T.J. Waldburger with his bout against Matthew Riddle at UFC 124. In an exciting standup fight, Pierson defeated Riddle via Unanimous Decision. UFC 124 was the first and last time fans were allowed to vote on Fight of the Night as the Welterweight title fight between George St. Pierre and Josh Koscheck was voted the Fight of the Night. Many non-casual UFC fans and Dana White felt that the Pierson vs. Riddle fight was the true Fight of the Night. Due to this, White announced that fight awards would be decided by the UFC and no the fans.

Pierson faced Jake Ellenberger at UFC 129. Pierson was caught with a quick counter that knocked him out at 2:42 in Round 1. Pierson again would face another difficult opponent at UFC 141, when he fought Don Hyun Kim. Pierson was defeated via Unanimous Decision.

Pierson bounced back from the two defeats when he faced Jake Hecht at UFC on FOX 3, on 8 June, 2012. He won via Unanimous Decision.

Pierson had expected to face Dan Miller, on 22 September, 2012 at UFC 152, but Miller pulled out due to personal reasons. Pierson instead faced Lance Benoist, who he defeated via Unanimous Decision.

In what was surely to be an exciting matchup Pierson was scheduled to faced Rick Story at UFC 158, but was forced to pull out citing an injury as the reason. He was replaced with Quinn Mulhem.

At UFC 161 Pierson fought his closest bout ever when he faced Kenny Robertson on 15 June, 2013. Pierson was badly hurt in the third round, but was able to maintain his conposure and win the fight via Majority Decision.

With his last fight happening over a year and a half ago, it is unclear if Pierson will ever enter the UFC ring again. Currently he is keeping busy at a instructor at Headrush Training Center in Toronto, Ontario; as their wrestling coach.

Early on in his UFC career Pierson came under flak from the Toronto Police Department when he signed with the UFC, as it is against regulations to have a secondary income. This was not the first time Pierson's MMA career has come under scrutiny by his primary work (Toronto Police Department), as his early career name was Sean "Pimp Daddy" Pierson. Pierson has since left the police force.

Outside of his coaching and fighting career, Pierson keeps active by working with fellow Canadian fighters, Sam Stout, Mark Hominick, and Matt Mitrione as part of an anti-bullying program in the Greater Toronto Area.

Pierson is also a professional video gamer; he has won many video game tournaments in Canada. He often does video game reviews on his blog.